This NIDDK Mentored Research Scientist Development Award application describes a 5-year training plan designed to allow me to gain additional skill and knowledge so that I can transition into an independent research scientist. In carrying out the proposed research, and by following my career development plan I will add to my scientific repertoire and acquire expertise in intestinal developmental biology. Using this newly acquired expertise in intestine development, I will establish a scientific niche that will set me apart from my mentors and pave the way to a robust, extramurally funded research program. The research proposed in this application will focus on understanding how the stem/progenitor cells in the embryonic intestine are specified and regulated using both traditional mouse genetics, and a novel in vitro system we have developed that allows us to generate human intestinal tissue in culture from human embryonic and induced pluripotent stem cells. Generation of human intestinal tissue in culture will allow for unprecedented studies of human intestinal development, homeostasis and disease. The specific aims are designed to test a model where Sox9 regulates early intestinal progenitor cells as they are restricted to the proliferative intervillus region of the developing intestine. Specific Aim 1 will investigate the embryonic development of human and mouse intestinal stem cells using lineage labeling and cell tracing experiments. Specific Aim 2 will determine the role of Sox9 in regulating embryonic development of the intervillus region in human and mouse intestine. Specific Aim 3 will investigate a suppressive role for Wnt signaling in establishment of the intervillus progenitor zone during development. Collectively, the research proposed here is in line with the Trans-NIH Report "Opportunities and Challenges in Digestive Diseases Research: Recommendations of the National Commission on Digestive Diseases" (2009) which states: "Uncovering the mechanisms that control development and differentiation of the digestive tract before birth and in neonatal life could generate new insights for regenerative therapies to treat digestive cancers and other diseases, as well as provide new insights into disease pathogenesis." The goal of this Mentored Research Scientist Development Award is to develop the expertise that will allow me to run an independent, funded research program that will contribute to improving human health and disease.